The present invention generally relates to a process for regulating the fuel/air ratio of internal combustion engines, and more particularly to a process for fuel/air regulation in which changes in catalyst conditions, for example, as the result of ageing, are compensated
German Published, Unexamined Patent Application 3,537,530 describes an arrangement for regulating the fuel/air ratio of an internal combustion engine. The fuel/air ratio supplied to the internal combustion engine is detected in a known way by an oxygen sensor arranged in an exhaust gas path. An output signal from the oxygen sensor is subsequently compared, in a comparator, with a value representing the ideal stoichiometric value of the fuel/air mixture, and the result is fed to a proportional-plus-integral (PI) control unit. From the input signal having two variables, this control unit generates a step/ramp function as an output signal. This signal is compared with a triangular pulse train, thereby generating square-wave pulses which activate an electromagnetic valve in order to make the fuel/air mixture richer or leaner.
The characteristics of the PI control unit can be varied in order to rapidly match the regulation to changed operating conditions, for example the acceleration of the internal combustion engine. However, the control system, although responding very quickly to changed operating conditions, nevertheless does not respond to changed catalyst conditions. These changes can occur, for example, as a result of the ageing of the catalyst. The lower conversion rate of the catalyst necessarily associated with ageing consequently cannot be compensated.
Thus, an object of the present invention is to provide a fuel/air regulation arrangement of the relevant generic type in such a way that changes in the catalyst, for example as a result of ageing, are compensated.
According to preferred embodiments of the invention, this and other objects are achieved by changing one or both of the characteristics of the PI control unit, that is to say changing the proportional sensitivity or the reset time, in dependence on the running distance of the catalyst, the regulation being matched as closely as possible to the state of ageing of the catalyst.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.